Nonlinear optical crystals with wide entire-molecular-phonon-free range

Abstract

The present application relates to a nonlinear optical crystal. According to the nonlinear optical crystal of the present application, very low phonon absorption in the low frequency THz region can be exhibited, high nonlinear optical characteristics, excellent terahertz generation efficiency, and a broad dimple-free spectrum.

Description

Technology Field

[0001] This application relates to a nonlinear optical crystal. Background Technology

[0002] Terahertz (THz) spectroscopy and imaging systems are highly useful for characterizing various organic and inorganic materials, as well as for sensors, climate, and biomedical applications. THz waves in the frequency range of 0.5 THz to 2.5 THz resonate with low-energy excitations of organic and inorganic materials, such as whole-molecular phonon oscillations and lattice phonon oscillations. These low-energy THz waves offer various opportunities, such as analyzing phonon-electron coupling in organic semiconductors and perovskites, identifying defects in crystalline materials, studying chirality, arrangement and conformation isomers, and polymorphs, and approaching the conductivity of (semiconductors). Furthermore, low-energy THz waves enable the formation of transient birefringence in liquids, spin control in (anti)ferromagnets, and applications in cancer diagnosis and treatment.

[0003] Among various THz generators, nonlinear optical crystals are very attractive because they are broadband and efficient THz wave generation can often be achieved in relatively simple collinear configurations using optical rectification or difference frequency generation. Conventional organic THz crystals often exhibit superior nonlinear optical susceptibility and better phase matching compared to inorganic THz crystals, e.g., ZnTe and GaP crystals, resulting in high optical-THz energy conversion efficiencies of up to several percent. It should be noted that LiNbO3 and other ferroelectric crystals, which form another group of inorganic THz generators, often require more complex phase matching configurations known as tilted pulse front pumping for efficient THz wave generation.

[0004] A significant drawback in both organic and inorganic nonlinear optical crystals is the presence of total molecular phonon vibrations and / or lattice phonon vibrations. In inorganic nonlinear optical crystals, lattice phonon resonance is much stronger than in organic nonlinear optical crystals, completely limiting the THz frequency range generated by the magnetic absorption of THz waves. Although organic nonlinear optical crystals exhibit relatively weak phonon resonance, many total molecular phonon vibrations occur in the THz frequency range, particularly low-energy vibrations in the range of 0.5 THz to 2.5 THz, which cannot be completely avoided.

[0005] This low-energy THz frequency range corresponds to the translational, sliding, and rotational motions of the entire constituent molecules and / or a large portion of those constituent molecules in organic nonlinear optical crystals. The self-absorption of low-energy THz waves generated in organic nonlinear optical crystals ultimately produces a spectral shape with many dimples and a strongly modulated pattern. For example, 2-(4-hydroxystyryl)-1-methylquinolinium 4-methylbenzenesulfonic acid (OHQ-T), one of the conventional organic crystals with high optical-THz conversion efficiency, exhibits strong dimples up to 2.5 THz in the generated THz spectrum, which originates from total molecular phonon vibrations in this range. Therefore, there is a need to develop new nonlinear optical crystals with suppressed total molecular phonon vibrations characterized by low absorption coefficients and / or a small number of phonon modes below 2.5 THz. The problem to be solved

[0006] The objective of the present application is to provide a nonlinear optical crystal that exhibits very low phonon absorption in the low frequency THz region, high nonlinear optical properties, excellent terahertz generation efficiency, and a broad dimple-free spectrum. means of solving the problem

[0007] To solve the above problem, the nonlinear optical crystal of the present application comprises a styrylquinolinium cation of the following chemical formula 1; and an anion of the following chemical formula 2 or the following chemical formula 3.

[0008] [Chemical Formula 1]

[0009]

[0010] (In the above chemical formula 1, any one of R1 to R3 is a halogen atom or an alkyl group having 1 to 3 carbon atoms, the remainder are each independently hydrogen, and R4 is a halogen atom)

[0011] [Chemical Formula 2]

[0012]

[0013] [Chemical Formula 3]

[0014]

[0015] (In the above Chemical Formula 2 or Chemical Formula 3, R5 and R6 are each independently selected from hydrogen, hydroxyl, halogen, nitro, formyl, carboxyl, alkyl, alkoxy, cycloalkyl, haloalkyl, aryl, haloaryl, heteroaryl, heterocycloalkyl, haloheteroaryl, alkenyl, haloalkenyl, alkynyl, haloalkynyl, haloalkoxy, keto, ketoaryl, haloketoaryl, ketoheteroaryl, ketoalkyl, haloketoalkyl, ketoalkenyl, haloketoalkenyl, phosphoalkyl, phosphonate, phosphate, phosphine, phosphine oxide, phosphoryl, phosphoaryl, sulfonyl, sulfoalkyl, sulfoarenyl, sulfonate, sulfate, sulfone, amine, polyether, silylalkyl, or silylalkyloxy, and if carbon is included, the number of carbon atoms It is within the range of 1 to 12, n is an integer from 0 to 5, and p is an integer from 0 to 7.

[0016] In the above chemical formula 1, R4 can be a chlorine atom or a fluorine atom.

[0017] In addition, in the above chemical formula 1, R4 may be a fluorine atom.

[0018] In addition, in the above chemical formula 1, any one of R1 to R3 may be an alkyl group having 1 to 3 carbon atoms.

[0019] In addition, in the above chemical formula 1, any one of R1 to R3 may be a methyl group.

[0020] In addition, the above anion may be the anion of Chemical Formula 2.

[0021] In addition, the above anion may be a benzene sulfonic acid anion of the following chemical formula 4.

[0022] [Chemical Formula 4]

[0023]

[0024] (In the above chemical formula 4, R7 is hydrogen, a C1 to C3 alkyl group, a halogen atom, a C1 to C3 alkoxy group, a C1 to C3 haloalkyl group, or a C1 to C3 haloalkoxy group)

[0025] In addition, in the above chemical formula 4, R7 may be a methoxy group.

[0026] In addition, the styrylquinolinium cation and the anion may have an orthogonal dipole bond structure. Effects of the invention

[0027] According to the nonlinear optical crystal of the present application, very low phonon absorption in the low frequency THz region can be exhibited, high nonlinear optical characteristics, excellent terahertz generation efficiency, and a broad dimple-free spectrum. Brief explanation of the drawing

[0028] Figure 1 is a graph showing the absorption spectra in methanol of the nonlinear optical crystals prepared in Example 1 and Example 2, respectively. Figures 2 and 3 are thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) heat diagrams of the nonlinear optical crystals prepared in Example 1 and Example 2, respectively. Figures 4 and 5 are graphs measuring whether powder second harmonic generation (SHG) occurred at a fundamental wavelength of 1300 nm for the OM7FQ-MBS crystal of Example 1 and the OM7ClQ-MBS crystal of Example 2, respectively. Figure 6 is a diagram showing the molecular ordering of the OM7FQ-MBS crystal of Example 1 along the crystallographic b-axis. Figure 7 is a diagram showing the molecular ordering of the OM7FQ-MBS crystal of Example 1 along the crystallographic c-axis. FIG. 8 is a diagram showing the orthogonal cation-anion dipole coupling assembly of the OM7FQ-MBS crystal of Example 1. FIG. 9 is a diagram showing a parallel cation-anion dipole coupling assembly of a conventional OMQ-MBS crystal and an OHQ-T crystal. Figures 10 and 11 respectively show the Hershfeld surface and fingerprint of an OM7FQ cation in atomic contact with F…all in the OM7FQ-MBS crystal of Example 1. Figure 12 shows the corresponding fingerprint of the OM7FQ cation with atomic contact with F…O in the OM7FQ-MBS crystal of Example 1. FIG. 13 shows the Hershfeld corresponding fingerprints of the OM7FQ cation and the OMQ cation, respectively, having atomic contact with C…C in the OM7FQ-MBS crystal of Example 1 and the conventional OMQ-MBS crystal. Figure 14 is a photograph of the OM7FQ-MBS single crystal of Example 1 grown in a saturated methanol solution at 40°C at a cooling rate of about 1°C / h using a cooling method. Figure 15 is a graph showing the reflected X-ray diffraction pattern of the OM7FQ-MBS single crystal of Example 1, grown in a saturated methanol solution at 40°C at a cooling rate of about 1°C / h using a cooling method. Figure 16 is a graph showing the molecular orientation of the OM7FQ-MBS single crystal of Example 1, grown in a saturated methanol solution at 40°C at a cooling rate of about 1°C / h using a cooling method. Figure 17 is a graph comparing the crystal density and void volume of conventional non-halogenated and fluorinated quinolinium cation-based THz crystals of the example. FIG. 18 is an absorption spectrum graph measured along the projection of the polar axis onto the (011) plane of the OM7FQ-MBS crystal of Example 1 grown in the THz frequency range. Figure 19 is an absorption spectrum graph of a conventional organic THz salt crystal having a parallel cation-anion dipole coupling assembly. Figure 20 is a graph of the THz spectrum generated from the OM7FQ-MBS crystal of Example 1 with a thickness of 0.1 mm. Figure 21 is a graph showing the THz amplitude according to the time domain in a 0.1 mm thick OM7FQ-MBS crystal of Example 1 pumped at 800 nm, a 0.46 mm thick conventional OHQ-T crystal, and a 0.22 mm thick conventional OMQ-MBS crystal. Figure 22 is a graph showing the THz amplitude according to the THz frequency in the 0.1 mm thick OM7FQ-MBS crystal of Example 1 pumped at 800 nm, the 0.46 mm thick conventional OHQ-T crystal, and the 0.22 mm thick conventional OMQ-MBS crystal. Specific details for implementing the invention

[0029] The nonlinear optical crystal of the present application is a crystal that can be used for nonlinear optical applications, specifically, as an organic crystal, comprising a styryl quinolinium cation of the following chemical formula 1 and an anion of the following chemical formula 2 or the following chemical formula 3. The nonlinear optical crystal according to one embodiment of the present application is a material in which, when a laser is irradiated, an electric field capable of causing perturbation between a nucleus and an electron is created, so the electric field does not respond linearly to the refractive index as before, but responds nonlinearly due to perturbation, thereby exhibiting phenomena such as the generation of a second harmonic that doubles the incident beam frequency, the addition of two waves, and the generation of a second frequency.

[0030] [Chemical Formula 1]

[0031]

[0032] In the above chemical formula 1, any one of R1 to R3 is a halogen atom or an alkyl group having 1 to 3 carbon atoms, the remainder are each independently hydrogen, and R4 is a halogen atom.

[0033] [Chemical Formula 2]

[0034]

[0035] [Chemical Formula 3]

[0036]

[0037] In the above Chemical Formula 2 or Chemical Formula 3, R5 and R6 are each independently one or more selected from hydrogen, hydroxyl, halogen, nitro, formyl, carboxyl, alkyl, alkoxy, cycloalkyl, haloalkyl, aryl, haloaryl, heteroaryl, heterocycloalkyl, haloheteroaryl, alkenyl, haloalkenyl, alkynyl, haloalkynyl, haloalkoxy, keto, ketoaryl, haloketoaryl, ketoheteroaryl, ketoalkyl, haloketoalkyl, ketoalkenyl, haloketoalkenyl, phosphoalkyl, phosphonate, phosphate, phosphine, phosphine oxide, phosphoryl, phosphoaryl, sulfonyl, sulfoalkyl, sulfoarenyl, sulfonate, sulfate, sulfone, amine, polyether, silylalkyl, or silylalkyloxy, and if carbon is included, the number of carbon atoms It is within the range of 1 to 12, n is an integer from 0 to 5, and p is an integer from 0 to 7.

[0038] According to the nonlinear optical crystal of the present application, very low phonon absorption in the low frequency THz region can be exhibited, high nonlinear optical characteristics, excellent terahertz generation efficiency, and a broad dimple-free spectrum.

[0039] In one example, in the above formula 1, any one of R1 to R3 may be an alkyl group having 1 to 3 carbon atoms. For example, the alkyl group having 1 to 3 carbon atoms may be a methyl group, an ethyl group, or a propyl group. In one embodiment, in the above formula 1, any one of R1 to R3 may be a methyl group. In this case, in the above formula 1, the remainder of R1 to R3 may each independently be hydrogen. The nonlinear optical crystal may have a non-centrosymmetric crystal structure by including the styrylquinolinium cation in which any one of R1 to R3 is an alkyl group having 1 to 3 carbon atoms, specifically a methyl group, and the remainder each independently has hydrogen, thereby reducing the symmetry of the cationic chromophore. As a result, the above nonlinear optical crystal exhibits very low phonon absorption in the low frequency THz region and can exhibit high nonlinear optical properties, excellent terahertz generation efficiency, and a broad dimple-free spectrum.

[0040] In another example, in Chemical Formula 1 above, R4 may be a halogen atom. In Chemical Formulas 1 to 3 above, the halogen atom may be, for example, a chlorine atom, a fluorine atom, a bromine atom, or an iodine atom. In one embodiment, R4 may be a chlorine atom or a fluorine atom. Specifically, R4 may be a fluorine atom. By having the aforementioned halogen atom, R4 of the styrylquinolinium cation not only exhibits an orthogonal cation-anion dipole coupling assembly with the anion, but also generates numerous secondary interactions between the styrylquinolinium cations. These strong interionic interactions can reduce void volume and increase crystal density, thereby suppressing molecular phonon vibrations.

[0041] In another example, the anion may be the anion of Chemical Formula 2. Since the description of the anion of Chemical Formula 2 is the same as described above, it will be omitted.

[0042] In another example, the anion may be a benzene sulfonic acid anion of the following chemical formula 4.

[0043] [Chemical Formula 4]

[0044]

[0045] In the above chemical formula 4, R7 is hydrogen, an alkyl group having 1 to 3 carbon atoms, a halogen atom, an alkoxy group having 1 to 3 carbon atoms, a haloalkyl group having 1 to 3 carbon atoms, or a haloalkoxy group having 1 to 3 carbon atoms.

[0046] For example, the above alkyl group having 1 to 3 carbon atoms may be a methyl group, an ethyl group, or a propyl group.

[0047] Additionally, the halogen atom may be a chlorine atom, a fluorine atom, a bromine atom, or an iodine atom. In one embodiment, R7 may be a chlorine atom or a bromine atom.

[0048] In addition, the alkoxy group having 1 to 3 carbon atoms may be a methoxy group, an ethoxy group, or a propoxy group. In one embodiment, R7 may be a methoxy group.

[0049] In addition, the carbon-1 to carbon-3 haloalkyl group may be a trifluoromethyl group, a trichloromethyl group, a pentafluoroethyl group, a pentachloroethyl group, a heptafluoropropyl group, or a heptachloropropyl group. In one embodiment, R5 may be a trifluoromethyl group. In one embodiment, R7 may be a trifluoromethyl group.

[0050] In addition, the above-mentioned haloalkoxy group having 1 to 3 carbon atoms may be a trifluoromethoxy group, a trichloromethoxy group, a pentafluoroethoxy group, a pentachloroethoxy group, a heptafluoropropoxy group, or a heptachloropropoxy group.

[0051] In one example, the styrylquinolinium cation and the anion may have an orthogonal dipole bonding structure. By having the styrylquinolinium cation and the anion have an orthogonal dipole bonding structure, the nonlinear optical crystal can reduce the void volume and increase the crystal density, thereby suppressing molecular phonon vibrations.

[0053] The present application will be described in more detail below through embodiments according to the present application and comparative examples not according to the present application, but the scope of the present application is not limited by the embodiments presented below.

[0055] Example 1

[0056] Manufacturing of nonlinear optical crystals

[0057] 1) OM7FQ-MBS Synthesis

[0058] 5 g (13.8 mmol) of 7-fluoro-1,2-dimethylquinolinium 4-methoxybenzenesulfonic acid and 1.87 g (13.8 mmol) of 4-hydroxy-3,5-dimethylbenzaldehyde were dissolved in 70 ml of methanol, and then condensed in the presence of 0.27 ml (2.75 mmol) of piperidine used as a catalyst to synthesize 7-fluoro-2-(4-hydroxy-3-methylstyryl)-1-methylquinolinium 4-methoxybenzenesulfonic acid (OM7FQ-MBS), a nonlinear optical crystal of the following chemical formula 5, with a yield of 8%.

[0059] [Chemical Formula 5]

[0060]

[0061] In the above chemical formula 5, R1 is a methyl group, R2 and R3 are each independently hydrogen, R4 is a fluorine atom, and R7 is a methoxy group.

[0063] 2) 1 H-NMR analysis

[0064] 1H-NMR(600 MHz, DMSO- d The data for 6, δ(ppm)) is as follows.

[0065] 10.39 (s, 1H, -OH), 8.96 (d, 1H, J = 9.0 Hz, C5H2N), 8.52 (d, 1H, J = 9.0 Hz, C4H3F), 8.43 (m, 1H, C5H2N), 8.43 (m, 1H, C4H3F), 8.20 (d, 1H, J = 15.2 Hz, CH), 7.86 (m, 1H, C4H3F), 7.86 (m, 1H, C6H3), 7.67 (m, 1H, C6H3), 7.67 (m, 1H, CH), 7.50 (d, 2H, J = 9.0 Hz, C6H4SO3 - ), 6.93 (d, 1H, J = 8.3 Hz, C6H3), 6.84 (d, 2H, J = 8.3 Hz, C6H4SO3 - ), 4.46 (s, 3H, NCH3), 3.74 (s, 3H, -OCH3), 2.21 (s, 3H, -CH3).

[0067] 3) 13 C-NMR analysis

[0068] 13 C NMR(DMSO- d The data for 6, δ) is as follows.

[0069] 165.86, 164.18, 159.79, 159.15, 157.21, 148.59, 142.89, 141.08, 140.78, 133.05, 131.95, 130.12, 127.02, 126.05, 125.16, 124.62, 119.98, 118.21, 115.16, 114.83, 112.69, 105.61, 55.12, 39.93, 15.91.

[0071] Example 2

[0072] Manufacturing of nonlinear optical crystals

[0073] 1) Synthesis of OM7ClQ-MBS

[0074] 5.97 g (15.7 mmol) of 7-chloro-1,2-dimethylquinolinium 4-methoxybenzenesulfonic acid and 2.14 g (15.7 mmol) of 4-hydroxy-3,5-dimethylbenzaldehyde were dissolved in 100 ml of methanol, and then condensed in the presence of 0.31 ml (0.53 mmol) of piperidine used as a catalyst to synthesize 7-chloro-2-(4-hydroxy-3-methylstyryl)-1-methylquinolinium 4-methoxybenzenesulfonic acid (OM7ClQ-MBS), a nonlinear optical crystal of the following chemical formula 6, with a yield of 38%.

[0075] [Chemical Formula 6]

[0076]

[0077] In the above chemical formula 6, R1 is a methyl group, R2 and R3 are each independently hydrogen, R4 is a chlorine atom, and R7 is a methoxy group.

[0079] 2) 1 H-NMR analysis

[0080] 1 H-NMR(600 MHz, DMSO- d The data for 6, δ(ppm)) is as follows.

[0081] 10.4 (s, 1H, -OH), 8.93 (d, 1H, J = 9.0 Hz, CHN), 8.66 (s, 1H, CHCl), 8.55 (d, 1H, J = 9.6 Hz, C4H3Cl), 8.32 (d, 1H, J = 9.0 Hz, C5H2N), 8.22 (d, 1H, J = 15.8 Hz, CH), 7.97 (dd, 1H, J= 8.6 Hz, C4H3Cl), 7.86 (s, 1H, C6H3), 7.67 (m, 2H, C6H3), 7.67 (m, 1H, CH), 7.50 (d, 2H, J = 9.0 Hz, C6H4SO3 - ), 6.92 (d, 1H, J = 8.3 Hz, C6H3), 6.84 (m, 2H, J = 9.0 Hz, C6H4SO3 - ), 4.48 (s, 3H, NCH3), 3.74 (s, 3H, -OCH3), 2.21 (s, 3H, -CH3).

[0083] 3) 13 C-NMR analysis

[0084] 13 C NMR(DMSO- d The data for 6, δ) is as follows.

[0085] 159.99, 159.13, 157.18, 149.01, 142.70, 141.17, 139.88, 139.39, 132.02, 131.64, 130.31, 129.07, 127.02, 126.08, 126.03, 125.28, 120.90, 118.97, 115.23, 114.77, 112.69, 55.12, 15.92.

[0087] Example 3

[0088] Manufacturing of nonlinear optical crystals

[0089] 1) Synthesis of OM7FQ-BBS

[0090] 1.93 g (4.7 mmol) of 7-fluoro-1,2-dimethylquinolinium 4-bromobenzenesulfonic acid and 0.65 g (4.7 mmol) of 4-hydroxy-3,5-dimethylbenzaldehyde were dissolved in 15 ml of methanol, and then condensed in the presence of 0.1 ml (0.9 mmol) of piperidine used as a catalyst to synthesize 7-fluoro-2-(4-hydroxy-3-methylstyryl)-1-methylquinolinium 4-bromobenzenesulfonic acid (OM7FQ-BBS), a nonlinear optical crystal of the following chemical formula 7, with a yield of 4%.

[0091] [Chemical Formula 7]

[0092]

[0093] In the above chemical formula 7, R1 is a methyl group, R2 and R3 are each independently hydrogen, R4 is a fluorine atom, and R7 is a bromine atom.

[0095] 2) 1 H-NMR analysis

[0096] 1 H-NMR(600 MHz, DMSO- d The data for 6, δ(ppm)) is as follows.

[0097] 10.43 (s, 1H, -OH), 8. 93 (d, 1H, J = 8.9 Hz, C5H2N), 8.51 (d, 1H, J = 9.6 Hz, C4H3F), 8.45 (m, 1H, C5H2N), 8.40 (m, 1H, C4H3F), 8.19 (d, 1H, J = 15.2 Hz, CH), 7.86 (m, 1H, C4H3F), 7.85 (m, 1H, C6H3), 7.68 (d, 1H, J = 15.8 Hz, CH), 7.65 (m, 1H, C6H3), 7.52 (d, 2H, J = 6.2 Hz, C6H4SO3 - ), 7.51 (d, 2H, J= 6.9 Hz, C6H4SO3 - ), 6.93 (d, 1H, J = 8.3 Hz, C6H3), 4.46 (s, 3H, NCH3), 2.28 (s, 3H, CH3), 2.21 (s, 3H, CH3).

[0099] 3) 13 C-NMR analysis

[0100] 13 C NMR(DMSO- d The data for 6, δ) is as follows.

[0101] 165.88, 164.20, 159.78, 157.24, 148.58, 147.65, 142.92, 140.80, 133.06, 131.96, 130.62, 130.10, 127.75, 126.07, 125.20, 124.63, 121.62, 119.99, 118.23, 115.17, 105.70, 105.52, 15.92.

[0103] Example 4

[0104] Manufacturing of nonlinear optical crystals

[0105] 1) Synthesis of OM7FQ-CBS

[0106] 2.48 g (6.7 mmol) of 7-fluoro-1,2-dimethylquinolinium 4-chlorobenzenesulfonic acid and 0.94 g (5.0 mmol) of 4-hydroxy-3,5-dimethylbenzaldehyde were dissolved in 15 ml of methanol, and then condensed in the presence of 0.1 ml (1.0 mmol) of piperidine used as a catalyst to synthesize 7-fluoro-2-(4-hydroxy-3-methylstyryl)-1-methylquinolinium 4-chlorobenzenesulfonic acid (OM7FQ-CBS), a nonlinear optical crystal of the following chemical formula 8, with a yield of 7%.

[0107] [Chemical Formula 8]

[0108]

[0109] In the above chemical formula 8, R1 is a methyl group, R2 and R3 are each independently hydrogen, R4 is a fluorine atom, and R7 is a chlorine atom.

[0111] 2) 1 H-NMR analysis

[0112] 1 H-NMR(600 MHz, DMSO- d The data for 6, δ(ppm)) is as follows.

[0113] 10.42 (s, 1H, -OH), 8.95 (d, 1H, J = 9.0 Hz, C5H2N), 8.52 (d, 1H, J = 9.6 Hz, C4H3F), 8.45 (m, 1H, C5H2N), 8.41 (m, 1H, C4H3F), 8.20 (d, 1H, J = 15.8 Hz, CH), 7.86 (m, 1H, C4H3F), 7.85 (m, 1H, C6H3), 7.67 (d, 1H, J = 15.2 Hz, CH), 7.65 (m, 1H, C6H3), 7.58 (d, 2H, J = 8.3 Hz, C6H4SO3 - ), 7.37 (d, 2H, J = 9.0 Hz, C6H4SO3 - ), 6.92 (d, 1H, J = 8.3 Hz, C6H3), 4.45 (s, 3H, NCH3), 2.21 (s, 3H, CH3).

[0115] 3) 13 C-NMR analysis

[0116] 13 C NMR(DMSO- d The data for 6, δ) is as follows.

[0117] 165.86, 164.18, 159.76, 157.12, 148.56, 147.17, 142.85, 140.70, 133.03, 131.95, 130.03, 127.71, 127.46, 125.99, 125.13, 124.58, 119.92, 118.18, 115.11, 114.74, 105.62, 105.43, 15.89.

[0119] Example 5

[0120] Manufacturing of nonlinear optical crystals

[0121] 1) Synthesis of OM7FQ-TFS

[0122] 2.0 g (5.0 mmol) of 7-fluoro-1,2-dimethylquinolinium 4-(trifluoromethyl)benzenesulfonic acid and 0.68 g (5.0 mmol) of 4-hydroxy-3,5-dimethylbenzaldehyde were dissolved in 15 ml of methanol, and then condensed in the presence of 0.1 ml (1.0 mmol) of piperidine used as a catalyst to synthesize 7-fluoro-2-(4-hydroxy-3-methylstyryl)-1-methylquinolinium 4-(trifluoromethyl)benzenesulfonic acid (OM7FQ-TFS), a nonlinear optical crystal of the following chemical formula 9, with a yield of 16%.

[0123] [Chemical Formula 9]

[0124]

[0125] In the above chemical formula 9, R1 is a methyl group, R2 and R3 are each independently hydrogen, R4 is a fluorine atom, and R7 is a trifluoromethyl group.

[0127] 2) 1 H-NMR analysis

[0128] 1 H-NMR(600 MHz, DMSO- d The data for 6, δ(ppm)) is as follows.

[0129] 10.42 (s, 1H, -OH), 8.84 (d, 1H, J= 9.0 Hz, C5H2N), 8.46 (d, 1H, J = 8.9 Hz, C4H3F), 8.38 (m, 1H, C5H2N), 8.34 (m, 1H, C4H3F), 8.17 (d, 1H, J = 15.8 Hz, CH), 7.80 (d, 1H, J = 14.4 Hz, CH), 7.79 (m, 1H, C4H3F), 7.78 (d, 2H, J = 8.3 Hz, C6H4SO3 - ), 7.70 (d, 2H, J = 8.3 Hz, C6H4SO3 - ), 7.64 (d, 1H, J = 8.3 Hz, C6H3), 7.56 (d, 1H, J = 8.3 Hz, C6H3), 4.39 (s, 3H, NCH3), 2.18 (s, 3H, CH3).

[0131] 3) 13 C-NMR analysis

[0132] 13 C NMR(DMSO- d The data for 6, δ) is as follows.

[0133] 165.88, 164.20, 160.02, 157.14, 152.07, 148.57, 142.81, 140.76, 133.03, 131.98, 130.14, 128.87, 126.36, 125.97, 125.07, 124.58, 123.27, 121.45, 119.95, 118.15, 114.93, 105.63, 105.44, 15.91.

[0135] Experimental Example 1. Design of a Halogenated Nonlinear Optical Crystal

[0136] The halogen-substituted styrylquinolinium cation (OM7FQ) of Example 1 and the styrylquinolinium cation (OM7ClQ) of Example 2 have a structure similar to the conventional non-halogenated cation chromophore, 2-(4-hydroxy-3-methylstyryl)-1-methylquinolinium (OMQ). The OMQ-based crystals having a 4-methoxybenzenesulfonate (MBS) anion exhibit efficient terahertz (THz) wave generation but show two absorption peaks in the low-frequency THz range (1.1 THz and 1.9 THz).

[0137] As shown in Examples 1 and 2, introducing halogenated substituents (-F and -Cl) to the OM7FQ and OM7ClQ cation chromophores can yield desired crystal properties through increased interionic interactions, reduced pore volume, and increased crystal density. Highly polar halogenated substituents (-F and -Cl) act as hydrogen bond acceptors and halogen bond donors and acceptors, generating numerous secondary interactions not only between cations and anions but also between cations. These strong interionic interactions can reduce pore volume and increase crystal density, which can lead to the suppression of molecular phonon vibrations. Additionally, crystal density can be higher if the halogenated substituents have a higher atomic weight compared to non-halogenated hydrogen substituents.

[0139] Experimental Example 2. Evaluation of Physical Properties

[0140] In the case of the styrylquinolinium cation (OM7FQ) chromophore of Example 1 and the styrylquinolinium cation (OM7ClQ) of Example 2, MBS anions were introduced similarly to conventional non-halogenated OMQ-MBS crystals. Figure 1 is a graph showing the absorption spectra in methanol of the nonlinear optical crystals prepared in Example 1 and Example 2, respectively. As shown in Figure 1, the OM7FQ-MBS crystal of Example 1 and the OM7ClQ-MBS crystal of Example 2 exhibit an orange color, and λ max= exhibited maximum absorption in methanol at 440 and 446 nm. Conventional OMQ-MBS crystals also showed maximum absorption (λ) similar to that of the nonlinear optical crystals of Examples 1 and 2. max It exhibited an orange color with a wavelength of 434 nm. This indicates that the HOMO-LUMO absorption band does not change significantly compared to the non-halogenated OMQ cation even when halogenated substituents (-F and -Cl) are introduced to the OM7FQ and OM7ClQ cations. Therefore, it can be expected that they possess similar molecular nonlinear optical properties according to the general nonlinearity-transparency trade-off. Both the OM7FQ-MBS crystal of Example 1 and the OM7ClQ-MBS crystal of Example 2 exhibit high thermal stability. Figures 2 and 3 are the thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) heat diagrams of the nonlinear optical crystals prepared in Example 1 and Example 2, respectively. As shown in Figures 2 and 3, the lowest phase transition temperature, melting temperature, and decomposition temperature all exceeded 230°C, confirming their suitability for practical applications. The melting temperatures of the nonlinear optical crystals of Example 1 and Example 2 were 280°C and 277°C, respectively, which were similar to the melting temperature of the conventional OMQ-MBS crystal, 285°C.

[0142] Experimental Example 3. Measurement of Second Harmonic Generation (SHG)

[0143] For the nonlinear optical crystal prepared in the example, qualitative SHG (second harmonic generation) was measured using an infrared pump with a center wavelength of 1300 nm, a pulse duration of 130 fs, and a power of 10 mW.

[0144] To achieve macroscopic second-order optical nonlinearity in a crystal, a non-centrosymmetric arrangement of cationic chromophores is required. Figures 4 and 5 are graphs measuring the presence of powder second harmonic generation (SHG) at a fundamental wavelength of 1300 nm for the OM7FQ-MBS crystal of Example 1 and the OM7ClQ-MBS crystal of Example 2, respectively. As shown in Figures 4 and 5, qualitative measurements of powder second harmonic generation (SHG) at a fundamental wavelength of 1300 nm confirmed that both the OM7FQ-MBS crystal of Example 1 and the OM7ClQ-MBS crystal of Example 2 exhibited clear SHG signals. Consequently, the OM7FQ-MBS crystal of Example 1 and the OM7ClQ-MBS crystal of Example 2 possess a non-centrosymmetric crystal structure. In addition to non-centrosymmetric molecular arrangement, good crystal growth capability is important for practical photonic applications. The OM7FQ-MBS crystal of Example 1 exhibited better crystal growth ability compared to the OM7ClQ-MBS crystal of Example 2. Using a solution cooling method, the OM7FQ-MBS single crystal of Example 1, which was large enough for X-ray single crystal structure analysis and optical experiments, could be successfully grown. However, the OM7ClQ-MBS crystal of Example 2, of a suitable size, could not be obtained using the same method. Therefore, it was confirmed that the OM7FQ-MBS single crystal of Example 1 simultaneously exhibited macroscopic optical nonlinearity and superior crystal growth ability compared to the OM7ClQ-MBS crystal of Example 2.

[0146] Experimental Example 4. Crystal Structure Analysis

[0147] 1) X-ray analysis

[0148] The structure of the nonlinear optical crystal prepared in the example was analyzed using X-rays.

[0149] In X-ray single crystal structure analysis, the OM7FQ-MBS crystal grown in Example 1 is non-centrosymmetric and triclinic. P1. Shows space group symmetry. Fig. 6 is a diagram showing the molecular ordering of the OM7FQ-MBS crystal of Example 1 along the crystallographic b-axis. Since there is only one OM7FQ cation chromophore in the unit cell (Z = 1), all chromophores are first-order hyperpolar. β max Molecular order angle between the direction and polar axes ( θ p It was perfectly parallel to ) being 0°. Consequently, the order parameter is maximum (cos 3 θ p = 1.0). As shown in Fig. 6, the primary hyperpolarity of the OM7FQ cation chromophore of Example 1 β max It was assumed that the orientation and value of were identical to the OMQ cation chromophore of a conventional OMQ-MBS crystal having the same crystal symmetry as the OM7FQ-MBS crystal of Example 1. The macroscopic optical nonlinearity of the OM7FQ-MBS crystal of Example 1 was significant ( β max cos 3 θ p = 121 Ⅹ 10 -30 This value was similar to many conventional organic THz crystals.

[0150] Meanwhile, the relative molecular orientation between the cation and the anion in the OM7FQ-MBS crystal of Example 1 was somewhat peculiar. Figure 7 is a diagram showing the molecular order of the OM7FQ-MBS crystal of Example 1 along the crystallographic c-axis. As shown in Figure 7, it was confirmed that in Example 1, the long molecular axis of the OM7FQ cation is orthogonal to the long molecular axis of the MBS anion, forming an orthogonal cation-anion dipole coupling assembly as shown in Figure 8. In contrast, as shown in Figure 9, in many conventional organic THz salt crystals, e.g., OMQ-MBS crystals and OHQ-T crystals, the long molecular axis of the cation chromophore is parallel to the long molecular axis of the molecular anion with a small rotation angle. In the most commonly used collinear THz generation configuration, the orthogonal cation-anion dipole coupled assembly of the organic THz salt crystal shown in Fig. 8 is advantageous in avoiding self-absorption of the generated THz waves compared to the parallel cation-anion dipole coupled assembly shown in Fig. 9. This advantage arises because the polarization direction of the generated THz waves is perpendicular to the long molecular axis of the molecular anion in the orthogonal cation-anion dipole coupled assembly. Therefore, the orthogonal cation-anion dipole coupled assembly of the OM7FQ-MBS crystal of Example 1 is expected to be highly advantageous in suppressing THz self-absorption, and smaller dimples occur in the generated THz spectrum.

[0151] In addition to the orthogonal cation-anion dipole coupling assembly, the fluorine (-F) substituent of the OM7FQ cation of Example 1 creates many secondary bonds that help suppress molecular phonon vibrations.

[0153] 2) Hirshfeld Surface and Fingerprint Analysis

[0154] Hershfeld surface and fingerprint analysis were performed on the nonlinear optical crystals prepared in the examples using the Crystal Explorer (ver. 21.5) program.

[0155] FIGS. 10 and FIGS. 11 respectively show the Hershfeld surface and fingerprint of an OM7FQ cation in atomic contact with F…all in the OM7FQ-MBS crystal of Example 1. In FIG. 10, the red dashed line indicates an F…all distance of less than 3.1 Å. FIG. 12 shows the corresponding fingerprint of an OM7FQ cation in atomic contact with F…O in the OM7FQ-MBS crystal of Example 1. FIG. 13 shows the corresponding Hershfeld fingerprints of the OM7FQ cation and the OMQ cation, respectively, in atomic contact with C…C in the OM7FQ-MBS crystal of Example 1 and the conventional OMQ-MBS crystal.

[0156] As shown in FIGS. 10 and 11, fluorine substituents serve as strong hydrogen bond donor sites. In addition, fluorine substituents also serve as halogen bond donor sites, and as shown in the F…O atomic contacts in FIGS. 10 and 12, F… - O3S-(3.02 Å) and -F…OH(2.95 Å) form halogen bonds.

[0157] Introducing a fluorine substituent to the OM7FQ cation of Example 1 alters the π-π stacking interactions between the cations. As shown in Fig. 13, in the C…C atomic contacts representing the frontal π-π stacking of the cation chromophore, the fluorinated OM7FQ-MBS crystal of Example 1 has a narrower frontal π-π stacking compared to the unfluorinated conventional OMQ-MBS crystal. Therefore, the OM7FQ-MBS crystal, having a unique orthogonal cation-anion dipole bond structure with a secondary bond to which a fluorine atom was introduced, can result in the suppression of phonon vibrations of the entire molecule.

[0159] Experimental Example 5. Evaluation of Ultra-Wideband Terahertz Wave Generation

[0160] Figure 14 is a photograph of the OM7FQ-MBS single crystal of Example 1 grown in a saturated methanol solution at 40°C at a cooling rate of approximately 1°C / h using a cooling method. Figure 15 is a graph showing the reflected X-ray diffraction pattern of the OM7FQ-MBS single crystal of Example 1 grown in a saturated methanol solution at 40°C at a cooling rate of approximately 1°C / h using a cooling method. Figure 16 is a graph showing the molecular orientation of the OM7FQ-MBS single crystal of Example 1 grown in a saturated methanol solution at 40°C at a cooling rate of approximately 1°C / h using a cooling method. Figure 17 is a graph comparing the crystal density and void volume of the conventional non-halogenated and fluorinated quinolinium cation-based THz crystals of the example.

[0161] As shown in FIG. 15, the largest surface of the grown OM7FQ-MBS single crystal of Example 1 is the (011) plane. As shown in FIG. 16, the polar axis of the grown OM7FQ-MBS single crystal of Example 1 is rotated approximately 29° from the (011) plane. When generating THz waves using the crystal grown without further processing, a preferred collinear configuration and the simplest normal pump incidence angle can be utilized. Using this configuration allows for the effective use of the diagonal macroscopic optical nonlinearity of the OM7FQ-MBS crystal of Example 1. The projection ratio of the polar axis to the (011) crystal plane is cos(29°) = 0.88. Additionally, as shown in FIG. 16, the polarization direction of the generated THz wave is at an angle of approximately 45°, which is significantly far from the long molecular axis of the MBS anion.

[0162] The OM7FQ-MBS crystal of Example 1 grown exhibits a broad overall molecular phonon-free range. FIG. 18 is a graph of the absorption spectrum measured along the projection of the polar axis onto the (011) plane of the OM7FQ-MBS crystal of Example 1 grown in the THz frequency range. As shown in FIG. 18, the OM7FQ-MBS crystal of Example 1 is 15 mm -1 It was confirmed that it exhibits a broad phonon-free range of 0.9 THz to 2.3 THz, defined by the absorption coefficients below. In contrast, many conventional organic THz salt crystals exhibit strong absorption peaks within the entire molecular phonon range of 0.5 THz to 2.5 THz. Figure 19 is an absorption spectrum graph of a conventional organic THz salt crystal having a parallel cation-anion dipole coupling assembly. In Figure 19, the conventional organic THz salt crystals are OHQ-T crystal, OMQ-MBS crystal, 2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium 4-methylbenzenesulfonic acid (HMQ-T) crystal, and 4-(4-(dimethylamino)styryl)-1-methylpyridinium 4-methylbenzenesulfonic acid (DAST) crystal. As shown in Fig. 19, the OHQ-T crystal exhibited strong and broad absorption in the range of 1 THz to 2 THz, and the DAST crystal exhibited strong absorption at 1.1 THz. It was confirmed that the absorption peaks of the OHQ-T and DAST crystals originated from total molecular phonon vibrations involving the movement of both cations and anions. Additionally, it was confirmed that multiple absorption peaks appeared in the HMQ-T crystal within the range of 0.5 THz to 2.5 THz.

[0163] It was confirmed that the THz absorption characteristics of the fluorinated OM7FQ-MBS crystal of Example 1 were significantly different compared to the non-fluorinated OMQ-MBS crystal, which exhibited two absorption peaks at 1.1 THz and 1.9 THz. This difference was identified as being due to distinct molecular ordering characteristics, as shown in Figures 7 to 9, namely the orthogonal cation-anion dipole coupling assembly of the OM7FQ-MBS crystal of Example 1 and the parallel cation-anion dipole coupling assembly of the conventional OMQ-MBS crystal. Furthermore, fluorine-induced interactions in the OM7FQ-MBS crystal of Example 1, as shown in Figures 10 to 13, may influence these changes. These interactions may lead to an increase in crystal density and a decrease in pore volume in the OM7FQ-MBS crystal of Example 1. The density of the OM7FQ-MBS crystal of Example 1 is 1.433 g / cm³. 3 As such, the density of conventional OMQ-MBS crystals is 1.373 g / cm³ 3 It is higher compared to. The pore volume of the OM7FQ-MBS crystal of Example 1 is 25.6%, whereas the pore volume of the conventional OMQ-MBS crystal is 27.1%. As shown in Fig. 17, when compared to other conventional non-halogenated quinolinium cations and the fluorinated quinolinium cation-based THz crystal of the example, it was confirmed that the OM7FQ-MBS crystal of Example 1 exhibits excellent crystal density and pore volume, which are advantageous for suppressing phonon vibrations.

[0164] FIG. 20 is a graph of the THz spectrum generated from the OM7FQ-MBS crystal of Example 1 with a thickness of 0.1 mm. For the generation of THz waves by optical rectification, an optical pump beam with a wavelength of 800 nm was used, with a pulse width of 130 fs, a repetition rate of 1 kHz, a pump power of 10 mW, and a beam diameter of 0.5 mm or less. For the detection of THz waves by electro-optical sampling (EOS), a ZnTe crystal with a thickness of 1.0 mm was used. In particular, the wavelength of many tabletop femtosecond (fs) laser systems is 800 nm. As shown in FIG. 20, the OM7FQ-MBS crystal of Example 1 generated a broad THz spectrum with a wide dimple-free flat spectral band in the range of 0.5 THz to 2.7 THz. It was confirmed that this broad spectrum is due to small absorption and a wide overall molecular phonon-free range of 0.9 THz to 2.3 THz as shown in Fig. 18.

[0165] In addition to a broad dimple-free flat spectral band, the OM7FQ-MBS crystal of Example 1 exhibits very high THz wave generation efficiency. For comparison, the OM7FQ-MBS crystal of Example 1, having an orthogonal cation-anion dipole coupled assembly, was subjected to a comparative study under the same experimental conditions as the conventional OHQ-T crystal and OMQ-MBS crystal, having a parallel cation-anion dipole coupled assembly. Figure 21 is a graph showing the THz amplitude over time domain in the 0.1 mm thick OM7FQ-MBS crystal of Example 1, the 0.46 mm thick conventional OHQ-T crystal, and the 0.22 mm thick conventional OMQ-MBS crystal, pumped at 800 nm. As shown in Fig. 21, it was confirmed that the peak-to-peak THz electric field of the OM7FQ-MBS crystal of Example 1 was 3.6 times and 2.0 times higher than that of the conventional OMQ-MBS crystal and OHQ-T crystal, respectively. Fig. 22 is a graph showing the THz amplitude according to the THz frequency in the 0.1 mm thick OM7FQ-MBS crystal of Example 1 pumped at 800 nm, the 0.46 mm thick conventional OHQ-T crystal, and the 0.22 mm thick conventional OMQ-MBS crystal. As shown in Fig. 22, it was confirmed that the spectral amplitude of the OM7FQ-MBS crystal of Example 1, that is, the integrated area of ​​the generated THz spectrum, was 2.5 times and 1.7 times higher than that of the conventional OMQ-MBS crystal and OHQ-T crystal, respectively.

[0166] As discussed above, the OM7FQ-MBS crystal of Example 1, the conventional OMQ-MBS crystal, and the conventional OHQ-T crystal all exhibit similar macroscopic optical nonlinearity (121 Ⅹ 10 -30Despite having ), the OM7FQ-MBS crystal of Example 1 exhibits a higher THz generation efficiency. This THz generation efficiency can be largely attributed to the low THz absorption behavior. As shown in Fig. 22, it was confirmed that the spectral dimple positions of the THz waves generated in all three crystals correlate with the absorption peak positions shown in Fig. 22. Therefore, the fluorinated OM7FQ-MBS crystal of Example 1 has a broad, dimple-free flat spectral band, which allows it to generate a strong THz electric field.

Claims

Claim 1 A nonlinear optical crystal having a non-centrosymmetric crystal structure comprising a styrylquinolinium cation of the following Chemical Formula 1; and an anion of the following Chemical Formula 2 or the following Chemical Formula 3. [Chemical Formula 1] (In the above Chemical Formula 1, any one of R1 to R3 is a halogen atom or an alkyl group having 1 to 3 carbon atoms, the remainder are each independently hydrogen, and R4 is a halogen atom)[Chemical Formula 2] [Chemical Formula 3] (In the above Chemical Formula 2 or Chemical Formula 3, R5 and R6 are each independently selected from hydrogen, hydroxyl, halogen, nitro, formyl, carboxyl, alkyl, alkoxy, cycloalkyl, haloalkyl, aryl, haloaryl, heteroaryl, heterocycloalkyl, haloheteroaryl, alkenyl, haloalkenyl, alkynyl, haloalkynyl, haloalkoxy, keto, ketoaryl, haloketoaryl, ketoheteroaryl, ketoalkyl, haloketoalkyl, ketoalkenyl, haloketoalkenyl, phosphoalkyl, phosphonate, phosphate, phosphine, phosphine oxide, phosphoryl, phosphoaryl, sulfonyl, sulfoalkyl, sulfoarenyl, sulfonate, sulfate, sulfone, amine, polyether, silylalkyl, or silylalkyloxy, and if carbon is included, the number of carbon atoms It is within the range of 1 to 12, n is an integer from 0 to 5, and p is an integer from 0 to 7. Claim 2 In claim 1, a nonlinear optical crystal in which R4 in Chemical Formula 1 is a chlorine atom or a fluorine atom. Claim 3 In claim 2, in the above chemical formula 1, R4 is a fluorine atom in a nonlinear optical crystal. Claim 4 A nonlinear optical crystal according to claim 1, wherein in the above chemical formula 1, any one of R1 to R3 is an alkyl group having 1 to 3 carbon atoms. Claim 5 A nonlinear optical crystal according to claim 1, wherein in the above chemical formula 1, any one of R1 to R3 is a methyl group. Claim 6 In claim 1, the anion is a nonlinear optical crystal that is an anion of the formula 2. Claim 7 In claim 1, the anion is a nonlinear optical crystal in which the anion is a benzene sulfonic acid anion of the following chemical formula 4. [Chemical Formula 4] (In the above chemical formula 4, R7 is hydrogen, a C1 to C3 alkyl group, a halogen atom, a C1 to C3 alkoxy group, a C1 to C3 haloalkyl group, or a C1 to C3 haloalkoxy group) Claim 8 In claim 7, a nonlinear optical crystal in the above chemical formula 4, wherein R7 is a methoxy group. Claim 9 In claim 1, the styrylquinolinium cation and the anion are a nonlinear optical crystal having an orthogonal dipole coupling structure.

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